This invention relates to a dual fuse holder for providing electrical circuitry protection to the supply side and the load side of an electrical utility distribution system, which may include, for example, low-current electrical devices. One exemplary use of the dual fuse holder is for protecting electrical equipment in a power line data communication system.
Over the past few decades, much interest has been placed on delivering data over reliable electrical networks. More recently, the power grid has emerged as a viable alternative to telephone and cable networks due to improved modulation techniques increasing data rates across the power lines. Power line communication (PLC) relies on the existing power grid infrastructure, thus significantly reducing the costs in implementing a data network. However, one cost associated with a PLC system involves the equipment at or near the customer premises that allows the customer to receive a radio frequency (RF) data signal from the power lines.
One problem in delivering the data signal across the power grid lines is that transformers damage the RF data signal. While a transformer is necessary for stepping down voltage to a customer useable level, a transformer also prevents or significantly inhibits the ability of a receiving device to recover a transmitted RF data signal. When transporting electricity from the electrical substation to the customer, typically the voltage may be stepped down through one or more transformers to power lines that lead into the customer's home, business, or building. In implementing a PLC system, the transformer is typically bypassed through separate equipment to preserve the RF data signal.
Conventionally, PLC systems are implemented using existing electrical utility distribution system equipment to bypass a transformer. FIG. 7 is a photograph of a PLC system 700 using such existing electrical utility distribution system equipment. A power line 702 is connected to a utility pole 704, and a choke bushing 706 is arranged on the power line 702. Two fused cutouts 710A and 710B are coupled to the choke bushing 706 through wires 708A and 708B, respectively. The two fused cutouts 710A and 710B include fuse devices 712A and 712B, respectively, which hold fuse links. A bracket 714 supports the two fused cutouts 710A and 710B. A coupler 716 is attached to the bracket 714 and coupled to the two fused cutouts 710A and 710B. A coaxial cable 718 is coupled to the coupler 716 and also connects to low voltage lines that lead into a building.
The fused cutouts 710A and 710B create an open circuit by switching through mechanical separation. The fused cutouts 710A and 710B are shown in a mechanically separated position. The mechanically separated condition may occur when a fuse door of the fused cutout is opened with a switch stick, when a fuse link is broken by pulling or pushing on a breaking device included in a tensioning device, or when the fuse links in the fuse devices 712A and 712B, respectively, are overloaded after receiving an electrical current greater than a rated electrical current level for the fuse link. In the first instance above, the mechanical separation de-energizes and isolates an electrical circuit without damaging the fuse link. In the latter two instances, the mechanical separation of the fused cutout occurs after the fuse is damaged: either manually by the breaking device or after the fuse link is overloaded. An overload causes the fuse link to melt and the fused cutouts 710A and 710B to separate due to a loss of tension on the fuse link.
One problem with using existing electrical utility distribution system equipment is the significant costs associated with using this equipment in a PLC system. The electrical utility distribution system equipment is designed to protect electrical utility power equipment, and does not cost effectively meet the needs of the PLC system. The fuses in conventional electrical utility system equipment are rated to protect against damaging electrical current surges in electrical power distribution, and are grossly oversized for PLC equipment. In PLC systems, the RF data signal electrical current is much smaller in comparison to the electrical current associated with electrical power distribution. What is needed is a fuse holder designed for the requirements of the PLC industry, rather than the electrical utility industry.